The present invention relates to a novel, highly water-absorptive soft contact lens, and more particularly to a high water-absorptive soft contact lens made of a copolymer prepared by copolymerizing an acrylate polymer or a methacrylate polymer (hereinafter referred to as "(meth)acrylate polymer") having hydrophilic groups and at least one polymerizable group and hydrophilic monomers as main components.
It has been well-known that among various materials for contact lens use, a material which swells and softens as a result of absorbing water, is preferred for obtaining a soft contact lens which is confortable to wear.
Material mainly composed of polyhydroxyalkyl methacrylate, polyvinylpyrrolidone, or the like has been used in the above mentioned materials. The material mainly composed of polyvinylpyrrolidone is excellent in water-absorptive property and gas-permeability, and has a high safety for eyes from the physiological point of view because oxygen physiologically required for the cornea is supplied enough from the open air to the cornea through water impregnated in a contact lens.
The material mainly composed of polyvinylpyrrolidone has excellent properties as mentioned above. However, because it has a high water content, it shows remarkable deterioration of dynamical properties when it is swollen with water, and consequently, it has a problem in durability, being easily damaged when formed into a lens.
In order to solve the above mentioned problems in durability, disclosed in Japanese Examined Patent Publication No. 43085/1982 is a method to produce a comb-type block polymer by introducing suitably a side chain having a size within a certain range of polymethyl methacrylate into the main chain of a hydrophilic polymer, thereby improving mechanical strength, while maintaining the preferable nature of the hydrophilic polymer.
However, the polymethyl methacrylate having a polymerizable group in one end of the molecule which is disclosed in above mentioned publication has the disadvantages in productivity. That is to say, it is difficult to control the reaction so as to produce only the polymethyl methacrylate in good efficiency in the industrial production thereof, particularly in large quantities, a mixture of a polymethyl methacrylate having a polymerizable grou in the molecular chain end and a polymethyl methacrylate not having a polymerizable group is apt to be produced. Accordingly, when a hydrophilic monomer is copolymerized with the polymethyl methacrylate, the produced comb-type block copolymer contains the polymethyl methacrylate not copolymerized with the hydrophilic monomer, thus the devitrification-phenomena may appear when the copolymer impregnated with water and the yield of the copolymer having good qualities is decreased.
The water content of the material mainly composed of polyhydroxyalkyl methacrylate is about 30 to 40% by weight, and therefore, this material is superior in the dynamical properties to the material mainly composed of polyvinylpyrrolidone. However, it has such problems that the water content is low and oxygen required for the cornea is not sufficiently supplied from the open air to the cornea through water impregnated in a contact lens.
The present invention is accomplished in order to obtain a highly water-absorptive soft contact lens which does not suffer remarkable deterioration of dynamical properties when it is swollen with water and which is excellent in transparency.